The present invention relates to a transversal filter comprising a charge shift device, wherein, on one surface of a substrate consisting of doped semiconductor material there is arranged a series of capacitor elements, each consisting of at least one insulating layer capacitor. For the operation of the filter, the outer or surface electrodes of each capacitor element are connected to one of a number of (at least two) shift pulse sequences which are displaced in phase relative to one another. The filter has a serial input to which the signal to be filtered is applied. In the case of capacitor elements intended for a selected member of the shift pulse trains, non-reactive amplifying outputs are provided which are connected to a filter output from which the signal to be filtered can be obtained. The amplification factor of each of these amplifying outputs corresponds to an assigned value of the pulse response of the filter function provided by the filter.
Transversal filters of the type described above are known (IEEE Journal of Solid-State Circuits, Vol. SC-8, No. 2, April 1973, pages 138 to 146 and Bell-Northern Research 11.4, pages 240 to 243). The charge shift devices consist of CCDs. The non-reactive, amplifying outputs can be achieved either by means of the so-called split-electrode method or by means of true amplifiers having high-ohmic input impedances. In the case of the split-electrode method, each relevant capacitor element consists of two insulating layer capacitors which are arranged next to one another and are coupled by means of a doped zone in the substrate. The capacitance ratio of these two insulating layer capacitors is selected in dependence upon the desired amplification factor. The non-reactive, amplifying outputs are provided only in the case of specific capacitor elements, and in fact only in those intended for one and the same predetermined shift pulse sequence. All the other non-reactive, amplifying outputs are connected to a filter output from which the filtered signal can be obtained. The amplification factor of each non-reactive amplifying output corresponds to an assigned value of the pulse response of the filter function which is to be provided by the filter.